Risk of contamination when planning psychological therapy trials can be assessed using a simple framework

The objective of this study was to develop and pilot a standard framework that could be used to assess risk of contamination in psychological therapy trials, at the protocol development stage.

We developed and piloted a risk of contamination framework on a sample of 100 psychological therapy trial protocols registered on the International Standard Randomised Controlled Trial Number (ISRCTN) registry (www.isrctn.com). We assessed all protocols as being low or high risk via three possible sources of contamination: 1) participants in the control arm, 2) participants in the intervention arm, 3) therapists in the intervention arm.

Overall, we found that the risk of contamination across all three sources was low for most studies (86 of 100 trial protocols; 86%). We identified 14 studies that had a potentially high risk for contamination. Most of these (N = 10) were identified as risk of contamination arising from a therapist in the intervention arm.

The risk of contamination framework we piloted in this study could be a helpful tool for researchers aiming to identify and manage risk of contamination in their trial protocol development. We found that the risk of contamination was relatively low in the psychological therapy trials we sampled for this study, as measured by our framework, and could usually be mitigated through reasonable adjustments to the study design.